The present invention relates to improvements in check valves (also known as one-way valves) which permit the flow of fluid media in a first direction but prevent a return flow of such media in a second direction counter to the first direction.
U.S. Pat. No. 4,227,533 A (granted Oct. 14, 1980 to Godfrey) discloses a check valve wherein the outlet is defined by a tube adapted to be flattened for the purpose of preventing return flow of a fluid toward and into the inlet. This valve constitutes a further development of so-called drain tube valves which are employed in certain types of watercraft, e.g., in power boats. A drawback of such valves is that the flattened regions of the deformed tubular outlet tend to accumulate solid matter which adheres to the outlet and reduces the rate of fluid flow through the valve and also prevents adequate sealing of the outlet when the latter should prevent a return flow of fluids, especially gaseous fluids. Similar drawbacks are exhibited by numerous other conventional check valves including, for example, that disclosed in U.S. Pat. No. 6,401,266 and in European patent application Serial No. EP1 174 549 A2 of Senteur (published Jan. 23, 2002 and relying on the priority of the Netherlands patent application Serial No. NL 1015745 filed Jul. 19, 2002).
The above discussed conventional valves exhibit the additional drawback that solid matter tends to accumulate along the edges of the flattened tube, i.e., in the regions where the resiliency of the tube is less pronounced than elsewhere. Such deposits of solid matter reduce the resiliency of the adjacent portion of the tube and cannot be readily removed therefrom. The deposits of solid matter on the tube can rapidly gather into accumulations which suffice to permit a backflow of gaseous fluids, e.g., of noxious gases which gather in sewage systems.
U.S. Pat. No. 4,084,606 (granted Apr. 18, 1978 to Mittleman) discloses a fluid transfer device employing a so-called umbrella check valve which has first and second inlets and a duckbill-shaped outlet. The valving element of this valve permits the flow of a fluid from the first inlet to the second inlet and from the second inlet to the outlet but blocks the flow of fluid from the second inlet to the first inlet as well as from the outlet to both inlets. This check valve is intended to serve as a means for regulating the administration of liquid medicaments to a patient. Each half of the duckbill-shaped outlet is at least partially rigid.
An additional drawback of all presently known check valves which are known to the applicant and employ tubular or duckbill-shaped outlet defining devices is that such devices tend to collapse when the pressure differential between the inner side and the exterior of the outlet reaches a certain relatively low value. This can result in undesirable sealing of the outlet when such sealing is not desirable or dangerous. Attempts to avoid such untimely collapse of the outlet were unsuccessful if the check valve is to remain sufficiently sensitive, e.g., to open in response to the flow of urine therethrough but to invariably prevent the flow of malodorous gases in a direction counter to the flow of urine.